1. Field of the Invention
This invention relates to a hydraulic lash adjuster, and more particularly to a hydraulic lash adjuster provided with a valve device for preventing external air from being drawn into a high pressure chamber of the adjuster when an engine is re-started.
2. Related Background Art
Heretofore, in ordinary internal combustion engines, in order to accommodate the difference between the expansion of a cylinder head by heat and the expansion of a valve mechanism, a hydraulic lash adjuster has been used to provide a proper, usually zero, valve clearance and to prevent both noise during the operation of the engine and horsepower loss by a draft of raw gas.
Further, it has been known to use such a lash adjuster to cause oil passing through the lash adjuster to be discharged from an oil outlet provided in the lash adjuster in order to lubricate the surface of contact of a swing arm with a cam and thereby prevent abrasion of the surface of contact.
The lash adjuster held in a cylinder block is disposed in intimate contact with the underside of one end of the swing arm so that the oil outlet of the lash adjuster is opposed to an oil injection port of the swing arm. One end of a poppet valve bears against the underside of the other end of the swing arm. Further, the camming surface of the cam rotatably bears against the upper surface of the swing arm to constitute a surface of contact therebetween.
The oil discharged from the oil outlet of the lash adjuster passes through the oil injection port of the swing arm and along the upper surface of the swing arm to said surface of contact. Thus, the surface of contact is lubricated by that oil. This is an improvement as compared with the case where the surface of contact was lubricated only by the lubricating oil from around the cam shaft.
However, a lash adjuster as just described is subject to problems due to air mixing air with the oil supplied thereto. When such oil enters a reservoir chamber, the oil having air mixed therewith in the reservoir chamber gradually moves from a check valve into a high pressure chamber because a slight amount of oil flowing out from a minute gap is supplied during each rotation of the cam shaft. As a result, the oil in the high pressure chamber becomes spongy, thus causing noise and impairing the function of the lash adjuster. The above-noted phenomenon becomes particularly noticeable when the engine oil is hot and the engine is revolving at a low speed.